06' Aveo Transmission jerks or hesitates intermittent at highway speed only

Hi Aveo people,
I have a 2006 aveo, Auto Trans, that i have been tinkering with. About 135K miles. Engine starts, idles, accelerates, decelerates normal. No codes. It shifts through all 4 gears normally (and torque lock). I recently dumped and refilled the transmission fluid. added a quart of Lucas transmission happy stuff.
When driving between 50 and 60 Mph the transmission will jerk or hesitate slightly, and at random. Its a small jerk. slight loss of power to the wheels for a fraction of a second and then normal.
At lower speeds it runs perfect. also at 60-75 it runs perfect.
Seems that it does it more when going uphill or more engine load is present.
I was thinking TPS sensor or something.. Seems to me that the computer is telling the transmission to misbehave. So i'm inclined to think its some sensor. Torque converter unlocking and relocking at random? what input tells the torque converter to lock?
I have read a ton of forums looking for clues. Nothing definite. some folks think bad ignition coil, plugs or wires. I'm not sure that makes sense. Also no codes to read.
Thanks in advance for any input.
Ryan

Ryan- did you ever solve this? I have the same issue with my kids' 2005 Aveo. It does a slight buck/stumble when trying to cruise along at highway speeds. When it's under load or out of overdrive it does not do it. But there's no way the 155k engine will last running it at 4000+ rpm all the time. LOL
We have changed plugs, cleaned throttle body, and the car is generally very well maintained (it got it's second timing belt at 125k). I feel that TPS should make the problem happen at all speeds when the throttle is in that position, but it does not. Also if the cam is not advancing properly it should throw a code, and I get none. That's why I am leaning towards transmission issue and the car is not worth diving into those repairs or replacement.

Luckily the car is mostly used for driving around town and is a cheap and reliable car for that purpose. It's just really annoying that we can't track this down. Anyone else have this happen and actually solve it?

Ugh, no one has had this issue? For less than $25 I replaced the TPS and that was not it. We also replaced the MAP sensor and that did not solve the issue. The only other 'inexpensive' item would be the TCC solenoid but that requires new trans gasket and I am not sure if the solenoid can even cause this symptom. I would think the only way this stuttering would happen is if the solenoid is 'leaky', but to me it seems like it should be an on or off situation for the valve. Maybe there's buildup inside the TCC solenoid valve??

Feel free to chime in. Please! ;)

UPDATE! One of the things we recently fixed was charging the AC system (which was weak when we bought it 3 years ago and just wasn't used the last couple summers) and as soon as I started running that extra load the car started misfiring badly with check engine light. It finally registered P0300 multi misfire code. Apparently the plug wires which had been replaced just before we bought the car were already failing. I never suspected the wires as the car has had less than 10k put on it in 3 years.
Apparently the stutter at highway speed was slight misfires that weren't generating any codes. The car rides fantastic now.